The present invention generally relates to an implantable ventricular cardioverter/defibrillator. The present invention more particularly relates to such a cardioverter/defibrillator which employs atrial pacing for preventing the induction of atrial fibrillation from ventricular cardioversion and defibrillation shocks.
There is an increasing problem with ventricular defibrillation and cardioversion shocks causing atrial fibrillation. This is due to the tendency towards the use of a xe2x80x9csingle-passxe2x80x9d lead, the use of a xe2x80x9chot canxe2x80x9d and the progressive decreasing of energy requirements for ventricular cardioversion and defibrillation. The single-pass lead, of the type known in the art, includes an atrial shock coil for positioning in the right atrium and a ventricular shock coil for positioning in the right ventricle. Hot can usage encompasses the use of the electrically conductive device enclosure as a common electrode wherein the cardioversion or defibrillation shocks are delivered from the atrial and ventricular shock coils to the electrically conductive device enclosure. Prior to the hot can approach, a subcutaneous patch electrode was used as the common electrode. With the single pass lead, the hot can approach causes more current flow through the atria than the subcutaneous patch electrode approach. The higher current though the atria can increase the probability of atrial fibrillation induction as a result of ventricular cardioversion and defibrillation
Extremely high-energy shocks cardiovert or defibrillate the entire heart so as to cardiovert or defibrillate both the atria and the ventricles to thus preclude induction of atrial fibrillation during ventricular cardioversion or defibrillation. However, the modern trend is to employ more moderate energy shocks for ventricular cardioversion and defibrillation. These energy levels may not cardiovert or defibrillate the atria during ventricular cardioversion and defibrillation thus frequently the atria is in fibrillation after ventricular cardioversion or defibrillation.
The induction of atrial fibrillation by ventricular arrhythmia shock therapy causes a cascading sequence of unfortunate problems. The delivery of the ventricular shock usually occurs during a period of patient unconsciousness and is not felt. However, after atrial fibrillation is induced, the patient is left with significant anxiety that there is still an arrhythmia. This can lead to inappropriate decisions on the part of the patient, as well as the implantable ventricular cardioverter/defibrillator. For example, the implanted device can mistake the atrial fibrillation for a ventricular arrhythmia and thus cause another shock to be delivered to the patient. This second shock is often extremely painful, because the patient will now be conscious. The second delivered shock, moreover, will most likely merely serve to ensure that the patient remains in atrial fibrillation.
The invention provides an implantable ventricular cardioverter/defibrillator for applying a quantity of electrical energy to a heart for terminating a ventricular arrhythmia while preventing the induction of atrial fibrillation. The cardioverter/defibrillator includes a ventricular arrhythmia detector that detects a ventricular arrhythmia, an atrial pacer that delivers atrial pacing pulses to an atrium of the heart responsive to the ventricular arrhythmia detector detecting a ventricular arrhythmia, and a generator that applies the electrical energy to the heart in timed relation to an atrial pacing pulse delivered by the atrial pacing means. The relative timing of the generator application and the atrial pacing pulse prevents the induction of atrial fibrillation.
The implantable ventricular cardioverter-defibrillator may further include a synchronizer that synchronizes the application of the electrical energy to the heart by the generator with a delivered atrial pacing pulse.
In accordance with a further aspect of the present invention, the ventricular arrhythmia detector may include a ventricular fibrillation detector and a ventricular tachycardia detector. As a further aspect of the present invention, a ventricular antitachycardia pacer, responsive to the ventricular tachycardia detector detecting ventricular tachycardia of the heart, applies antitachycardia pacing pulses to a ventricle of the heart. An analyzer determines if the antitachycardia pacing pulses terminate the detected ventricular tachycardia. If the ventricular tachycardia is not terminated by the antitachycardia pacing, the analyzer activates the atrial pacer and generator.
In accordance with a further aspect of the present invention, the implantable ventricular cardioverter/defibrillator may include a ventricular activation detector adapted to detect ventricular activations of the heart. The atrial pacer, responsive to the ventricular activation detector, delivers the atrial pacing pulses synchronized to detected ventricular activations.
In accordance with a further aspect of the present invention, if the ventricular fibrillation detector detects ventricular fibrillation, the atrial pacer delivers the atrial pacing pulses at a substantially fixed rate. Further, the generator may include a storage capacitor and a charger that begins charging the storage capacitor to a given energy upon the detection of ventricular fibrillation and the generator applies the electrical energy to the heart from the storage capacitor when the storage capacitor is charged to the given energy.
The invention further provides a method of terminating a ventricular arrhythmia of a heart while preventing the induction of atrial fibrillation. The method includes the steps of detecting a ventricular arrhythmia, delivering atrial pacing pulses to an atrium of the heart upon detecting a ventricular arrhythmia, and applying a quantity of electrical energy to the heart in timed relation to a delivered atrial pacing pulse.